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I don't understand gyroscopes


Dropship
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In a youtube vid, a guy shows us how difficult it is to lift a big heavy non-spinning gyroscope, but after it's spun up he can easily pick it up with one hand and whirl it around his head!

Where has its weight gone?

 

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8 hours ago, Dropship said:

In a youtube vid, a guy shows us how difficult it is to lift a big heavy non-spinning gyroscope, but after it's spun up he can easily pick it up with one hand and whirl it around his head!

Where has its weight gone?

 

A YouTube video is a bad place to start. YouTube is full of crap.

A spinning gyroscope weighs the same as a stationary one, so if your video suggests otherwise that is false. The special property of a spinning gyroscope is that if you try to change the direction of its axis of spin, it will tend to move at right angles to the change you are trying to making. For instance if it is upright in front of you and you push the top away from you it will move to the left or right, depending on the direction of spin.

It's hard to visualise why, but you can make sense of it by considering the momentum of 2 bits of the spinning rotor, on opposite sides of the axis, when an attempt is made to change the direction of the axis of spin. Bit hard to explain in detail without a diagram, though.  

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1 hour ago, exchemist said:

A YouTube video is a bad place to start. YouTube is full of crap.

A spinning gyroscope weighs the same as a stationary one, so if your video suggests otherwise that is false. The special property of a spinning gyroscope is that if you try to change the direction of its axis of spin, it will tend to move at right angles to the change you are trying to making. For instance if it is upright in front of you and you push the top away from you it will move to the left or right, depending on the direction of spin.

It's hard to visualise why, but you can make sense of it by considering the momentum of 2 bits of the spinning rotor, on opposite sides of the axis, when an attempt is made to change the direction of the axis of spin. Bit hard to explain in detail without a diagram, though.  

I'm quite positive that the OP is talking about this video:

 

No, it doesn't suggest that the weight changes. It is a pretty good demonstration and is followed by explanation.

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11 hours ago, Dropship said:

Where has its weight gone?

It didn't go anywhere. You can leverage the angular momentum and torque, as Derek explains in the followup. Notice the path of the apparatus - he's not lifting straight up.

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29 minutes ago, Genady said:

I'm quite positive that the OP is talking about this video:

 

No, it doesn't suggest that the weight changes. It is a pretty good demonstration and is followed by explanation.

Ah so he's pushing it round in a circle, is he? So the combined total of the force needed to push it round, plus the lifting force from his hand will equal the weight, I suppose. In other words he still has to exert a force equal to its weight, but not purely vertically, due to the reaction of the gyroscope. 

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2 minutes ago, exchemist said:

Ah so he's pushing it round in a circle, is he? So the combined total of the force needed to push it round, plus the lifting force from his hand will equal the weight, I suppose. In other words he still has to exert a force equal to its weight, but not purely vertically, due to the reaction of the gyroscope. 

The vertical force he exert is equal to the weight. However, the weight itself, i.e. the heavy wheel doesn't stay above his head. If we look only at the vertical displacement of the wheel, it goes up and then down.

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Thanks guys, and as a matter of interest I often wonder if scientists have ever done eperiments with gyros to explore their properties more deeply, such as by rigidly coupling a bunch of them together at various angles then spinning up the whole caboodle to note any effects.

For example i've heard it suggested they could somehow be used to create an anti-gravity power source. "  

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10 hours ago, Dropship said:

Thanks guys, and as a matter of interest I often wonder if scientists have ever done eperiments with gyros to explore their properties more deeply, such as by rigidly coupling a bunch of them together at various angles then spinning up the whole caboodle to note any effects.

For example i've heard it suggested they could somehow be used to create an anti-gravity power source. "  

Are you really an ex-physicist?

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3 hours ago, exchemist said:

Are you really an ex-physicist?

Yes I'm a shatterer of worlds like the rest of 'em..:)

I've also got an interest in other fields but they don't grab me as much, for example chemistry is too smelly, and biology is too stomach-churning.

PS- I do however take a healthy interest in theology and am fascinated by the 'Superscience' throughout the bible, for example Ezekiel's sighting of a flying craft that looked like "wheels within wheels" could be a gyroscope-powered thing..:)  

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51 minutes ago, Dropship said:

Yes I'm a shatterer of worlds like the rest of 'em..:)

I've also got an interest in other fields but they don't grab me as much, for example chemistry is too smelly, and biology is too stomach-churning.

PS- I do however take a healthy interest in theology and am fascinated by the 'Superscience' throughout the bible, for example Ezekiel's sighting of a flying craft that looked like "wheels within wheels" could be a gyroscope-powered thing..:)  

Oh dear. It doesn't look as if you are the ideal person to discuss science with, then. But thanks for the discussion topics: always fun to think about. 

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One of the non-intuitive aspects of gyroscopic motion is that any acceleration is perpendicular to the applied force.

If you spin a bicycle wheel then whack it sideways, it accelerates (turns) 90 degrees away, in both directions. That's why when you're riding a bike you can recover from a sideways jolt, by controlling the resulting torque with the handlebars.

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...which steers the bike underneath the centre of mass of the bike rider system...with an extremely small gyroscopic effect from the spinning wheels

On 3/11/2022 at 7:29 AM, swansont said:

It didn't go anywhere. You can leverage the angular momentum and torque, as Derek explains in the followup. Notice the path of the apparatus - he's not lifting straight up.

+1

This is the key...same vertical force (on average) but it's easier bio-mechanically. The weight feels less even though it isn't.

Also gives a slight relief of the vertical force through the "sticking point" of mechanical disadvantage for his arm, which he can make up for afterward when his arm is straighter vertically. Somewhat analogous to the way weightlifters use momentum in a clean and jerk to get by sticking points, but here they can pay later rather than upfront, with the weight raising delayed while the arm raises the light end.

Edited by J.C.MacSwell
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